How to Design Schemas in BigQuery

Why does schema design matter in BigQuery?

Well-planned schemas lower storage costs, speed up queries, and simplify maintenance. Bad schemas force expensive scans, complicate joins, and create data silos.

How do I create a new table schema?

Use CREATE TABLE with column names, data types, and optional partitioning and clustering clauses. Always match data types to the source system to avoid costly casts.

Example: Customers table

CREATE TABLE myshop.Customers (
id INT64,
name STRING,
email STRING,
created_at TIMESTAMP
) PARTITION BY DATE(created_at);


When should I use partitioning?

Partition on a column heavily used in WHERE filters, typically DATE or TIMESTAMP. For event or order data, partition by order date to restrict scans to relevant days.

When should I add clustering?

Cluster on columns frequently used in equality filters or joins, like customer_id. Clustering further prunes data blocks after partition pruning completes.

Example: Orders table

CREATE TABLE myshop.Orders (
id INT64,
customer_id INT64,
order_date DATE,
total_amount NUMERIC
) PARTITION BY order_date
CLUSTER BY customer_id;


How do I model one-to-many relationships?

Keep separate tables and join when needed. For Orders → OrderItems use INT64 foreign keys. Repeated nested records are possible but hinder cross-table analysis.

What are best practices for data types?

Prefer INT64 for IDs, NUMERIC for currency, STRING for free text, and TIMESTAMP/DATE for temporal data. Avoid FLOAT64 for money to prevent rounding errors.

How do I evolve a schema safely?

Add nullable columns with ALTER TABLE ... ADD COLUMN. Backfill values in a separate job. To drop columns, create a new table and copy only required fields.

What common naming conventions work best?

Use lowercase snake_case for tables and columns. Prefix surrogate keys with id, e.g., customer_id. Keep dataset names short, like myshop.

How do I test a schema design?

Load a sample data set, run representative queries, and review bytes_processed in the query plan. Iterate on partition and clustering choices until scans fall within acceptable limits.